Japanese Patent Application Laid-Open No. H11-294879 discloses a conventional motor-driven turbo compressor (hereinafter referred to as compressor). The compressor includes a housing, an electric motor, a rotating shaft, a first impeller, and a second impeller.
In the housing, a first impeller chamber, a second impeller chamber, and a motor chamber are formed. The first impeller chamber is located on one end side of the housing. The second impeller chamber is located on the other end side of the housing. The motor chamber is located between the first impeller chamber and the second impeller chamber. In the housing, a first suction port, a second suction port, a first discharge chamber, and a second discharge chamber are formed. The first suction port extends in the axial direction of the rotating shaft on one end side of the housing and communicates with the first impeller chamber. The second suction port extends in the axial direction of the rotating shaft on the other end side of the housing and communicates with the second impeller chamber. The first discharge chamber communicates with the first impeller chamber via a first diffuser. The second discharge chamber communicates with the second impeller chamber via a second diffuser.
Further, a first communication path and a second communication path are connected to the housing. The first communication path communicates with the first discharge chamber on one end side and communicates with the motor chamber on the other end side while extending to the outside of the housing. The second communication path communicates with the motor chamber on one end side and communicates with the second suction port on the other end side while extending to the outside of the housing.
The rotating shaft is rotatably supported by the housing and is capable rotating in the first impeller chamber and the second impeller chamber. The electric motor is accommodated in the motor chamber and drives to rotate the rotating shaft. The first impeller and the second impeller are arranged across the electric motor. Large diameter portions of the first and second impellers are faced to each other.
The first impeller is coupled to one end of the rotating shaft. The first impeller increases kinetic energy of a refrigerant in the first impeller chamber by rotating of the first impeller. Thereafter, the first impeller converts the kinetic energy of the refrigerant into pressure energy through the first diffuser, and compresses the refrigerant, and discharges the compressed refrigerant to the first discharge chamber. The second impeller is coupled to the other end of the rotating shaft. The second impeller increases kinetic energy of the refrigerant in the second impeller chamber by rotating of the second impeller. Thereafter, the second impeller converts the kinetic energy of the refrigerant into pressure energy through the second diffuser, and compresses the refrigerant, and discharges the compressed refrigerant to the second discharge chamber.
In the compressor, the refrigerant is sucked from the first suction port. The refrigerant is discharged to the first discharge chamber through the first impeller chamber and the first diffuser. Thereafter, the refrigerant is introduced into the motor chamber through the first communication path. The refrigerant is sucked from the motor chamber into the second suction port through the second communication path and discharged to the second discharge chamber through the second impeller chamber and the second diffuser. In this way, the refrigerant is compressed in two stages.
In this case, since the large diameter portion of the first impeller is located on the motor chamber side, a first thrust force for urging the rotating shaft to be drawn into the first impeller chamber is generated. Since the large diameter portion of the second impeller is also located on the motor chamber side, a second thrust force for urging the rotating shaft to be drawn into the second impeller chamber is generated. That is, the first thrust force and the second thrust force can offset each other. Here, it is also possible to set a difference between the outer diameter of the first impeller and the outer diameter of the second impeller to reduce a resultant force of the first and second thrust forces as much as possible. In this case, since a thrust bearing can be reduced in size, it is possible to realize a reduction in manufacturing costs and a reduction in the size of the compressor.
Further, in the compressor, since the refrigerant discharged to the first discharge chamber is introduced into the motor chamber by the first communication path, it is possible to cool the electric motor. Therefore, it is possible to attain improvement of durability of the electric motor.
However, in the compressor, the first discharge chamber and the motor chamber communicate with each other through the first communication path extending to the outside of the housing. The motor chamber and the second suction port communicate with each other through the second communication path extending to the outside of the housing. Therefore, the first and second communication paths project from the outer circumferential surface of the housing. A reduction in the size of the body diameter of the compressor is spoiled.
Further, in the compressor, the first impeller chamber, the first diffuser, and the first discharge chamber are formed on one end side of the housing. The second impeller chamber, the second diffuser, and the second discharge chamber are formed on the other end side of the housing. Therefore, both of the first communication path and the second communication path are inevitably long in the axial direction. Therefore, in the compressor, an increase in the axial length also occurs. Channel resistance of the refrigerant is large. There is also concern about a power loss.
The present invention has been devised in view of the circumstances in the past and it is a problem to be solved by the invention to provide a motor-driven turbo compressor in which a power loss hardly occurs while a reduction in manufacturing costs, a reduction in size, and improvement of durability are surely realized.